As semiconductor device dimensions get smaller, and device density increases, it becomes more and more difficult to build an efficient and reliable isolation process to separate active devices. One drawback with the LOCal Oxidation of Silicon (LOCOS) is the decreasing pad thickness which makes etch steps more difficult.
The process of the present invention provides a new nitride etch that is suitable for etching submicron features, and that stops on a thin pad oxide without substantially pitting the underlying silicon. These characteristics make the process of the present invention well suited for use in the conventional LOCOS process.
A lot of ion bombardment is used in the process of the present invention to cause the desired chemical reactions, hence this etch is more physical than chemical in nature. Because the etch is more physical, there is a lot less "loading."
"Loading" refers to uneven etching of the wafer. If there is less "loading, then the "open" and "tight" areas will etch at substantially the same rate. "Open" refers to the less confined spaces of the semiconductor device, such as the periphery of the device or the scribe lines, which tend to etch at a faster rate than "tight" areas. "Tight" refers to the more constricted areas of the semiconductor device, such as the area within the array and the runners between transistors.
Further, with the process of the present invention, there is no significant center to edge "loading" effect. Center to edge "loading" effect refers to a characteristic nonuniformity in etching wherein the center of a wafer etches at a slower rate than the edges, thereby resulting in a wafer which is thicker in the center than at the edges. If there is very little center to edge "loading" effect, then the etch uniformity across the wafer will be very good.
Other manufacturers are currently using CF.sub.4, CHF.sub.3 chemistries or other types of fluorine containing chemistries, if they perform a nitride etch in their fabrication processes.
These and other known processes suffer from either poor "loading" effects, poor uniformity, or poor nitride to oxide selectivity, which will make these processes inadequate for etching submicron nitride features.